Mitsubishi Electric FR-A700 Technical Manual page 454

1) Formula for calculating the acceleration and
deceleration times (simple method)
Shortest
tas =
acceleration time
Shortest
tds =
deceleration time
where,
J All J = motorJ + loadJ
T : M
(converted to an equivalent JM at the motor
2
shaft) [kg m ]
N:Difference between motor speeds before and
after acceleration/deceleration N
T Rated motor torque
M:
9550
T
M =
N
T max:Maximum load torque (converted to an
L
equivalent JM at the motor shaft) [N m]
T min: Minimum load torque (converted to an
L
equivalent JM at the motor shaft) [N m]
α
a : Acceleration torque coefficient
β: Brake torque coefficient regenerative braking
torque *
P: Rated motor torque [kW]
N: Motor synchronous speed at 60Hz [r/min]
* Refer to the Technical Note No.30 (data part)
2) Calculation and setting
acceleration and deceleration times ([Pr. 7, Pr. 8])
Set the time to accelerate/decelerate using
acceleration/deceleration
([Pr. 20]) as reference in acceleration/deceleration
time ([Pr. 7, Pr. 8]). Use "tas" and "tds" found in 1)
to calculate the acceleration and deceleration
times ([Pr. 7, Pr. 8]) at shortest acceleration/
deceleration time as follows:
Acceleration time ([Pr. 7]) =
Acceleration time ([Pr. 8]) =
Acceleration/deceleration
120
reference frequency ([Pr. 20])
N =
Number of motor poles
Speed at the output of
Acceleration/deceleration
N
reference frequency ([Pr. 20])
N
1
N
2
0
tas tds
ta td
Acceleration time ([Pr. 7])
Deceleration time ([Pr. 8])
When fast response is required, set the smallest
value of which the formula is satisfied. And when
J N
T
(T α a - T max)
9.55
M L
J N
T
(T β + T min)
9.55
M L
L
N [r/min]
1 - 2
P
[N m]
*
example of the
reference frequency
N
tas
N - N
1 2
N
tds
N - N
1 2
ta
td
soft acceleration / deceleration is required, set
the required time.
[Example 2] Calculated in the conventional unit system
[s]
A conveyor is driven by the SF-JR 2.2kW 4P motor and
FR-A720-2.2K inverter (V/F control).
Suppose that
[s]
JM = 0.008 [kg m2],
JL = 0.038 [kg m2],
TLmax = 9.8 [N m],
TLmin = 5.88 [N m], and the acceleration and deceleration
times are as short as possible.
JT = 0.008 + 0.038 = 0.046 [kg m2]
N = N1 - N2 =
(When the acceleration/deceleration reference
frequency is the initial setting of 60Hz.)
9550
TM =
From Technical Note No. 30 (data part)
supposing that the torque boost is large,
a = 1.15
tas =
9.55
= 1.0
tds =
9.55
When [Pr. 20 = 60Hz], acceleration time/deceleration time
setting is as follows.
Acceleration time ([Pr. 7]) =
Deceleration time ([Pr. 7]) =
Therefore set 2.4s or more for acceleration time, and 0.5s or
more for deceleration time.
(3) When there is a limit on acceleration
time
common
When acceleration time exceeds the required value,
select either Advanced magnetic flux vector control
or Real sensorless vector control, increase torque
boost, or select an inverter larger in capacity to
increase the inverter current overload capacity at
acceleration. Or, select a motor larger in capacity
(select an inverter larger in capacity also) to increase
the motor acceleration torque.
488
SELECTION
120 60
- 0 = 1800[r/min]
4
2.2
= 11.67[N m]
1800
0.046 1800
= 2.39[s]
(11.67 1.15 - 9.8)
0.046 1800
= 0.49[s]
(11.67 1.0 + 5.88)
1800
2.39 = 2.39
1800 - 0
1800
0.49 = 0.49
1800 - 0